Structure composed of elements and method for its production

ABSTRACT

The invention relates to a structure put together from elements, the elements forming a topological self-interlocking entity. To improve structures of this type, the invention proposes a self-supporting structure comprising hollow, tubular elements ( 1 ), which are put together with parallel axes to form a self-interlocking entity without any binder as a composite layer, in which the elements ( 1 ), respectively lying only loosely against one another with linear contact, are held together by a frame ( 2 ) or the like extending around the element structure and determining the flexural elasticity of the structure by its own restraining force, each of the elements ( 1 ) having in central cross section a circular cross section ( 3 ), starting from the circumference of which the generated surfaces of the element ( 1 ), respectively forming half, go over in an arcuately curved manner to the two element ends, the edge contour ( 4 ) of which respectively has the form of a flat ellipse having pointed major-axis vertices ( 5 ), the major axes ( 7, 8 ) of which, lying normal to the longitudinal axis ( 6 ) of the element, are turned by 90° with respect to each other about the longitudinal axis ( 6 ) of the element, the axial ratio of the two ellipse axes ( 7, 8 ) in a cross section lying normal to the longitudinal axis ( 6 ) of the element increasing continuously from the center of the element ( 1 ) respectively to its ends.

[0001] The invention relates to a structure composed of elements, the elements forming a topological self-interlocking entity.

[0002] In the article “Toughening by Fragmentation—How Topology Helps” in Advanced Engineering Materials 2001, 3 No. 11, pages 885-888, the fundamentals of a topological self-interlocking entity are described.

[0003] The invention is based on the object of developing structures of this type which are self-supporting and comprise identical elements which are put together without connecting elements or binders and have a favorable surface-area/volume ratio. They are intended primarily to replace structures put together by means of a joining technique, which have weak points and/or undesired stress concentrations, for example when aggressive media are used.

[0004] This object is achieved according to the invention by a self-supporting structure comprising hollow, tubular elements, which are put together with parallel axes to form a self-interlocking entity without any binder as a composite layer, in which the elements, respectively lying only loosely against one another with linear contact, are held together by a frame or the like extending around the element structure and determining the flexural elasticity of the structure by its own restraining force, each of the elements having in central cross section a circular cross section, starting from the circumference of which the generated surfaces of the element, respectively forming half, go over in an arcuately curved manner to the two element ends, the edge contour of which respectively has the form of a flat ellipse having pointed major-axis vertices, the major axes of which, lying normal to the longitudinal axis of the element, are turned by 90° with respect to each other about the longitudinal axis of the element, the axial ratio of the two ellipse axes in a cross section lying normal to the longitudinal axis of the element increasing continuously from the center of the element respectively to its ends.

[0005] The invention is also based on the object of using a suitable method for producing the structures according to the invention.

[0006] This object is achieved by a method which is characterized according to the invention by a computational breakdown of the structure into a number of layers, by successive application of layers of metal or ceramic powder particles and by subsequent selective laser sintering.

[0007] This method operates on the principle of rapid tooling, which is understood as meaning the production of forms, in particular tools, by the methods of rapid prototyping. Rapid prototyping as a generic term covers all the production methods which make it possible to generate models from 3D CAD data. As a difference from conventional methods, in which the form is produced by removal of material, this objective is achieved in the case of most RP methods by the build-up of material layer by layer. A major feature of this is the direct conversion of 3D CAD designs into material models. The rapid tooling process sequence is in this case made up of the following steps:

[0008] CAD design of the component preparation of the CAD data for the building process

[0009] building process

[0010] desired or required finishing operations.

[0011] After the design, the finished CAD data record must be prepared appropriately for machining. Work is then preferably based on the direct metal-laser sintering process, in which the energy of a CO₂ laser initially melts the scanned regions of a planar metal powder bed (corresponding to the layer information concerning the component). The liquefied powder particles bond to one another as a result and solidify to form a solid structure.

[0012] By the method described above, an entire self-supporting structure can be produced according to the invention simultaneously from different materials, such as for example metals or ceramics, it being possible for the density of the material to be varied. It is consequently unnecessary to produce the hollow, tubular elements individually.

[0013] The method comprises quite generally the production of all structures which comprises [sic] interlocked elements, it being possible to use both individual elements and elements arranged on a substrate or grown out of them [sic]. This includes the method in which such elements are applied layer by layer and the material is subsequently consolidated, with a computational breakdown of the self-supporting structure to be generated taking place. Alternative techniques for applying the elements or the material which comprises corresponding elements, such as for example metal or ceramic powder particles, are all the lithographic processes, the application of a gaseous or liquid phase, including a physical coating, for example by vapor deposition or sputtering, and also chemical vapor deposition (CVD), lamination with etching of suitable patterns, etc.

[0014] When the method described above is used for producing a self-supporting structure according to the invention, said structure is first broken down computationally into a number of layers and then built up layer by layer by successive application of layers of powder particles (for example metal or ceramic powder) and subsequent laser sintering. In this case, it is most important that component parts of individual elements in each layer do not sinter to one another, so that each tubular element in the composed structure is not bonded with its neighbors but merely fixed geometrically by the integration into neighboring elements.

[0015] In the case of the self-supporting structure built up according to the invention, it is not possible to remove an individual element from the composite layer on account of the topological self-interlocking. Since this would not apply to the elements arranged in an edge row of the structure, the frame extending around the element structure is provided according to the invention.

[0016] The individual elements may have different wall thicknesses, a thin-walled formation being advantageous for the creation of a large surface area with low mass. Moreover, the elements may have any desired configuration of their inner surface.

[0017] The structures according to the invention have a high flexural flexibility and are characterized by a large surface-area/mass ratio. With the aid of the production method explained above, a high porosity of the element walls can also be brought about in a specifically selective manner, whereby the surface area/mass ratio is increased still further and, if need be, a high permeability is achieved. In the case of the latter formation, at least some elements may be filled with an active substance.

[0018] Elements may consist of different materials. Furthermore, some elements may have a double length and consequently serve for anchoring structures lying one on top of the other.

[0019] In one possible embodiment, the frame may be rigidly formed and have a clamping device, which reduces the size of the interior space enclosed by the frame and receiving the elements. In principle, however, it is also possible for the frame to be elastically formed, its restraining force having to be adequate to ensure a certain flexural elasticity of the self-supporting structure.

[0020] With elements of different lengths, curved structures can also be formed.

[0021] Structures formed according to the invention can be used in particular in the construction and mechanical engineering sector for controlled sound damping or insulation; these structures can, however, also be used with preference for catalysts, filters, chemical reactors or baffles.

[0022] An embodiment of the invention serving as an example is represented in the drawing, in which:

[0023]FIG. 1 shows a self-supporting structure comprising hollow, tubular elements enclosed by a rigid frame, in plan view;

[0024]FIG. 2 shows the frame according to FIG. 1 in an isometric representation;

[0025]FIG. 3 shows the structure according to FIG. 1 in an isometric representation;

[0026]FIG. 4 shows a central cross section of the structure according to FIG. 3 in a representation according to FIG. 3 and

[0027]FIG. 5 shows the structure according to FIG. 3 in plan view.

[0028]FIG. 1 shows a self-supporting structure comprising hollow, tubular elements 1 which are put together with parallel axes to form a self-interlocking entity without any binder as a composite layer, in which the elements 1, respectively lying only loosely against one another with linear contact, are held together by a frame 2 extending around the element structure and determining the flexural elasticity of the structure by its own restraining force.

[0029]FIG. 2 shows the frame 2, the inner contour of which is adapted to the outer contour of the edge layers of the structure formed by the elements 1.

[0030] FIGS. 3-5 reveal the form of the identically formed tubular elements 1. Each of the elements 1 accordingly has in central cross section a circular cross section 3 (see FIG. 4), starting from the circumference of which the generated surfaces of the element 1, respectively forming half, go over in an arcuately curved manner to the two element ends, the edge contour 4 of which respectively has the form of a flat ellipse having pointed major-axis vertices 5, the major axes 7, 8 of which, lying normal to the longitudinal axis 6 of the element, are turned by 90° with respect to each other about the longitudinal axis 6 of the element, the axial ratio of the two ellipse axes 7, 8 in a cross section lying normal to the longitudinal axis 6 of the element increasing continuously from the center of the element 1 respectively to its ends. 

1. Self-supporting structure comprising hollow, tubular elements (1), which are put together with parallel axes to form a self interlocking entity without any binder as a composite layer, in which the elements (1), respectively lying only loosely against one another with linear contact, are held together by a frame (2) or the like extending around the element structure and determining the flexural elasticity of the structure by its own restraining force, each of the elements (1) having in central cross section a circular cross section (3), starting from the circumference of which the generated surfaces of the element (1), respectively forming half, go over in an arcuately curved manner to the two element ends, the edge contour (4) of which respectively has the form of a flat ellipse having pointed major-axis vertices (5), the major axes (7, 8) of which, lying normal to the longitudinal axis (6) of the element, are turned by 90° with respect to each other about the longitudinal axis (6) of the element, the axial ratio of the two ellipse axes (7, 8) in a cross section lying normal to the longitudinal axis (6) of the element increasing continuously from the center of the element (1) respectively to its ends.
 2. Self-supporting structure according to claim 1, characterized by different wall thicknesses of the individual elements (1).
 3. Self-supporting structure according to claim 1 or 2, characterized by a thin-walled formation of the elements (1) for the creation of a large surface area with low mass.
 4. Self-supporting structure according to claim 1, 2 or 3, characterized in that the elements (1) consist of different materials.
 5. Self-supporting structure according to one of the preceding claims, characterized in that at least some elements (1) are filled with an active substance and consist of a material of high permeability.
 6. Self-supporting structure according to one of the preceding claims, characterized by any desired configuration of the inner surface of the elements (1).
 7. Self-supporting structure according to one of the preceding claims, characterized in that some elements (1) have a double length (1) and serve for anchoring structures lying one on top of the other.
 8. Self-supporting structure according to one of the preceding claims, characterized in that the frame (2) is rigidly formed and has a clamping device, which reduces the size of the interior space enclosed by the frame (2) and receiving the elements (1).
 9. Self-supporting structure according to one of claims 1 to 7, characterized in that the frame is elastically formed.
 10. Self-supporting structure according to one of the preceding claims, characterized by elements (1) of different lengths (1) for forming curved structures.
 11. Method for producing a self-supporting structure according to one of the preceding claims, characterized by a computational breakdown of the structure into a number of layers, by successive application of layers of metal or ceramic powder particles and by subsequent selective laser sintering.
 12. Use of a self-supporting structure according to one of claims 1 to 10 in the construction and mechanical engineering sector for controlled sound damping or insulation.
 13. Use of a self-supporting structure according to one of claims 1 to 10 for catalysis, filters, chemical reactors or baffles. 